Some magnetic resonance imaging (MRI) applications desire both high resolution and high frame rates. Consider imaging a beating heart—high resolution would facilitate improved diagnosis while high frame rates would facilitate improved motion artifact avoidance by acquiring an image while the heart is at rest in between contractions. Motions other than heart contractions (e.g., respiration) can also complicate cardiac and other imaging. Therefore improvement in frame rates that do not sacrifice resolution, and improvements in resolution that do not sacrifice frame rates, are constantly being sought. One way to improve frame rates is to increase the degree of under-sampling.
Acquiring a magnetic resonance (MR) image may include acquiring both calibration data and image data. Acquiring adequate calibration data facilitates under-sampling image data and yet still achieving acceptable resolution. However, in some cases, acquiring fully-sampled calibration data sets may consume as much or more time than acquiring data for an MR image. Thus, applications like acquiring a full three dimensional (3D) multi-phase (CINE) data set of the heart in a single breath hold may be particularly challenging due, for example, to the time required to acquire fully-sampled data sets.
Conventionally, a single breath hold may only have allowed imaging a single slice of the heart. When multiple slices were required, multiple breath holds were required. Multiple breath holds may be challenging for patients that are having their heart imaged. Additionally, a patient may hold their breath differently on different breath hold attempts and thus images acquired during the different breath holds may be inconsistent. A further complication occurs as data is acquired further and further away from the time at which the calibration data was acquired.
High resolution and high frame rates are also sought after in dynamic MRI. Dynamic MRI (dMRI) involves creating a sequence of MR images to monitor temporal changes in an object of interest (e.g., tissue structure). dMRI apparatus seek to acquire images as fast as possible while maintaining a sufficient signal-to-noise ratio (SNR) to investigate the object being imaged.